1. Field of the Invention
The present invention is in the field of vapor plates used to cover manholes of transport tankers, such as an over-the-road tank trailer and tank railcars.
2. Description of Related Art
Vapor plates are utilized to cover the manhole of a tanker trailer or railcar when filling the tanker with the desired cargo. Commonly transported liquid cargo may be volatile and/or hazardous, such as liquid propane, gasoline, oil, liquefied natural gas, asphalt, industrial chemicals or acids. Other liquid cargo may not be hazardous, but may require maintaining sanitary conditions, such as milk, vegetable oils, other food oils, juices, or other items. Further, many dry goods which are commonly transported in such tankers may create a fine dust which may cause respiratory problems for workers when filling the tanks up with the dry cargo. A vapor plate plays an important role in keeping the volatile or hazardous gases in the tank or, alternatively, the un-sanitized airborne contaminants out.
Particularly, as used in the petroleum and chemical industries, the vapor plate keeps the gasoline or chemical vapors within the tank and may also prevent the build-up of excess vapor by allowing vapor removal using a vapor recovery system. Keeping the vapor from escaping the tank through the vapor plate is important for at least the following reasons: (1) the health of the operator, (2) environmental protection, (3) general safety (for example preventing build-up of flammable gases), and (4) satisfying industrial or governmental regulations. In other industries, vapor plates may also be important for protecting the safety of the food supply.
However, given the importance of keeping vapors in or contaminants out of the tanker in view of the harmful effects listed above, existing vapor plates have continually been found to perform insufficiently over their functioning lives. Existing vapor plates can generally comprise a plate having threaded rods extending through which are threadably engaged to the plate. The threaded rods generally have an appendage at the bottom of the threaded rod that can be raised and lowered to engage and release the appendage against the bottom of a rim of a manhole on a tank trailer or railcar. The appendage is raised and lowered by a user generally turning a handle at the top of the threaded rod and adjusting a threaded collar.
Threaded rods can be made of softer steel than many other steel components in order to economically manufacture a tooled threaded rod. The softer material can result in the threaded rod bending at some point during its functional life, particularly early on. Any bending of the threaded rod negatively impacts the function and performance of the vapor plate. The threaded push rod also has other shortcomings. As the threaded rod repeatedly passes through the threads in the existing vapor plate, any protective coating on the material wears off resulting in corrosion of the threads which results in the loss of material. In addition, if the collar is even a slightly different steel grade than the threaded rod, with either a higher or lower strength, the threads in the collar or on the threaded rod can wear down, again resulting in a loss of material. Further, the bending of the rod alters the thread distance at the bend. These frequently occurring losses of material or changes in the thread distance can create a passageway for vapors or gas to leak through the threads and vapor plate out of, or into, the tank.